An electrolytic solution circulation type battery such as a redox flow battery (RF battery) is a large capacity storage battery that stores power derived from natural energy obtained by photovoltaic power generation, wind power generation, or the like. An RF battery, which is typically connected, through an AC/DC converter, between a power generation unit (such as photovoltaic power generating equipment, wind power generation equipment, or a general power plant) and a load (such as a consumer), charges and stores electricity generated by the power generation unit and discharges and supplies stored electricity to the load.
For example, as shown in FIG. 4 which is an operating principle diagram for an RF battery, an RF battery 100 includes a battery cell 10 which is separated into a positive electrode cell 12 and a negative electrode cell 11 by a separator 11 that allows hydrogen ions to permeate. The positive electrode cell 12 contains a positive electrode 14 and is connected to a positive electrode electrolyte tank 20 that stores a positive electrode electrolyte via a circulation passage including a supply flow path 30 and a discharge flow path 32. Similarly, the negative electrode cell 13 contains a negative electrode 15 and is connected to a negative electrode electrolyte tank 21 that stores a negative electrode electrolyte via a circulation passage including a supply flow path 31 and a discharge flow path 33.
The electrolytes in the positive electrode electrolyte tank 20 and the negative electrode electrolyte tank 21 are supplied from the supply flow paths 30 and 31 to the cells 12 and 13 by pumps 34 and 35 provided in the middle of the supply flow paths 30 and 31, discharged from the cells 12 and 13 through the discharge flow paths 32 and 33 to the positive electrode electrolyte tank 20 and the negative electrode electrolyte tank 21, and thus circulated within the cells 12 and 13, respectively. While circulating the electrolytes in such a manner, charging and discharging are performed using the difference in oxidation-reduction potential between ions contained in the positive electrode electrolyte and ions contained in the negative electrode electrolyte. In FIG. 4, vanadium ions are shown as ions contained in the electrode electrolytes. Solid line arrows indicate charging and dashed line arrows indicate discharging.
In order to prevent oxidation of the electrolytes, the positive electrode electrolyte tank 20 and the negative electrode electrolyte tank 21 are hermetically sealed such that entry of the air is blocked. The pressure of a gas phase portion 20g or 21g in the positive electrode electrolyte tank 20 or negative electrode electrolyte tank 21 becomes negative (less than the atmospheric pressure) when the temperature of the gas phase portion 20g or 21g decreases or the liquid surface of the electrolyte falls at the start of circulation to increase the volume of the gas phase portion 20g or 21g. On the other hand, the pressure of the gas phase portion 20g or 21g in the positive electrode electrolyte tank 20 or negative electrode electrolyte tank 21 becomes positive (greater than the atmospheric pressure) when the temperature of the electrolyte increases or the volume of the gas phase portion 20g or 21g decreases. When the positive electrode electrolyte tank 20 or negative electrode electrolyte tank 21 excessively deforms (expands/contracts) as a result of the positive pressure/negative pressure, there is a concern that the positive electrode electrolyte tank 20 or negative electrode electrolyte tank 21 may be damaged. In particular, when deformation (expansion/contraction) occurs repeatedly, the positive electrode electrolyte tank 20 or negative electrode electrolyte tank 21 is likely to be damaged.
For example, as shown in FIG. 4, in PTL 1, a breathing bag (pressure adjustment bag) 110 is provided in each of the gas phase portions 20g and 21g of the positive electrode electrolyte tank 20 and the negative electrode electrolyte tank 21, the breathing bag (pressure adjustment bag) 110 being suspended from the top wall of each of the positive electrode electrolyte tank 20 and the negative electrode electrolyte tank 21 (refer to PTL 1). The inside of the breathing bag 110 communicates with the atmosphere. When the pressure of the gas phase portion 20g or 21g becomes negative, the breathing bag 110 takes in the atmosphere and expands to reduce the volume of the gas phase portion 20g or 21g, thereby increasing the pressure of the gas phase portion 20g or 21g. On the other hand, when the pressure of the gas phase portion 20g or 21g becomes positive, the breathing bag 110 discharges the internal gas to the atmosphere and contracts to increase the volume of the gas phase portion 20g or 21g, thereby decreasing the pressure of the gas phase portion 20g or 21g. In such a manner, it is possible to suppress the expansion/contraction of the positive electrode electrolyte tank 20 or negative electrode electrolyte tank 21 as a result of the positive pressure/negative pressure of the gas phase portion 20g or 21g. 